In a convoy travel of multiple vehicles forming an organized group of vehicles, following vehicles (i.e., “followers”) in a convoy which follow a leader vehicle (i.e., a “leader”) respectively receive travel information directly from the leader vehicle for performing vehicle travel control and organizing a convoy. Such a technique is disclosed, for example, in Japanese Patent Laid-Open No. 2009-239585 (JP '585). According to such technique, the following vehicles other than an immediate following vehicle (i.e., a right-behind vehicle) of the leader vehicle are also enabled to perform travel control that quickly reflects the travel information of the leader vehicle.
When multiple follower vehicles of the convoy directly receive the travel information transmitted from the leader vehicle of the convoy, the number of vehicles in the convoy is restricted based on the number of vehicles that can be covered by the capacity of the wireless communication unit of the leader vehicle.